Antenna positioner for portable satellite terminal

ABSTRACT

A motorized antenna positioning mechanism in a portable microwave communication unit for use as a ground station in a satellite communication system. The antenna positioner has compact and low profile azimuth wire drive mechanics, azimuth and polarization angle sensors that are not affected by slippage and backlash, and an elevation drive mechanism which neutralizes the pressure on the motor axis due to the weight of the parabolic antenna.

RELATED APPLICATIONS

The present application claims the benefit of U.S. patent application Ser. No. 11/220,549, filed Sep. 8, 2005.

FIELD OF THE INVENTION

The present invention relates to antenna positioning systems in certain types of portable terminals for satellite communications where automatic, rather than manual, alignment to the desired satellite is preferred.

BACKGROUND OF THE INVENTION

Typically, such terminals are found in Satellite News Gathering (SNG) and in some military communication systems. Because of the performance required, terminals of this kind are not intrinsically very small, as parabolic antennas around 1m in diameter are needed. This, in conjunction with the automatic acquisition feature, results in certain mechanical and electrical requirements on the positioner that this invention solves in a novel way.

In antenna positioners, or positioning systems, the mechanisms for adjusting the azimuth, elevation and polarization angles are typically conceptually different although the azimuth and elevation mechanisms usually share a common physical platform. The polarization angle may be adjusted by rotating the whole antenna but it is more common to rotate only the feed in which case the polarisation mechanism is completely separate from the other two. In addition to the purely mechanical aspects, there is also the issue of angular sensors for azimuth, elevation and polarization. Thus in discussing prior art, it is best to comment on these items separately.

Re azimuth:

Many motorized azimuth drives are based on the simple concept of the antenna being mounted on a rotational platform with the motor driving the platform via gears or cables with pulleys. Conceptually, the simplest arrangement involves a driving pulley on the axle of the motor, driving a circular plate via a flexible cable or “wire”. The axles of the motor and the driven plate are normally parallel. This can be modified depending on the specific application. The applicant has identified several US patents, using various embodiments of this basic principle such as e.g. U.S. Pat. No. 2,516,092, U.S. Pat. No. 2,787,169, U.S. Pat. No. 3,194,080, U.S. Pat. No. 4,210,094 etc. Of these, U.S. Pat. No. 2,787,169 is one that specifically applies to antenna control, using a combination of pulleys and long cables to control a TV antenna.

When the rotational platform carries a relatively heavy item, such as e.g. a 1-meter parabolic antenna with its boom and RF equipment, concerns arise as to the ability of the azimuth control mechanism to drive such a load without slippage. This gave rise to several patents that use what is essentially a screw as the driving element on which the cable is wound in multiple turns, with multiple turns on the periphery of the driven circular plate, or drum, as well. The drum periphery can have grooves, or it can be smooth. An example of the former is U.S. Pat. No. 4,351,197. U.S. Pat. No. 4,757,727 deals with a related subject, namely the termination of the cable on the drum. U.S. Pat. No. 4,787,259 goes further in that it uses several driving elements (motors with pulleys) to drive one rotating platform. U.S. Pat. No. 5,105,672 is similar to U.S. Pat. No. 4,351,197 with the difference of using a drum with smooth outer peripheral surface on which the cable is helically wound.

The multi-turn structures described in the prior art mentioned above enable turns greater than 360 degrees. This is not necessary for the azimuth control of a satellite terminal. Further, the disadvantage of the above solutions is that the multi-turn devices used result in relatively big (deep) structures compared to the simple one-turn pulley and drum combination.

Re elevation:

Many different mechanisms for motorized elevation adjustment are used in the prior art. Most of them use gears in various configurations, some use belts. A good example of a geared system for a parabolic antenna is shown in U.S. Pat. No. 4,725,843. A gear on the motor axle engages a sector gear mounted on a horizontal rotating shaft whose ends are fixedly attached to the antenna. As the motor turns, the shaft turns and thus the antenna turns, changing the elevation angle. U.S. Pat. No. 6,049,306 shows another example of a geared system, designed for a flat antenna, with more conventional gears. U.S. Pat. No. 6,937,299 uses a belt attached at one end to the boom and at the other to the back of the reflector, while the bottom part of the reflector is mounted on a pivot point. U.S. Pat. No. 6,188,367 uses a similar concept.

EP1465288, which discloses means for manual elevation adjustment, involves a long threaded rod that passes through what is essentially a large nut in a horizontal rotating shaft, appropriately affixed to the antenna structure. As the rod is turned, the nut moves up or down and the antenna inclines thus changing the elevation angle. This approach can be modified for use in a motorized assembly by adding a motor driving the elevation rod either directly or through intermediate gears. As in other systems, direct coupling is preferable as it avoids potential problems due to backlash in a geared system.

One of the problems in motorized elevation adjustment structures is the pressure exerted on the motor axle due to the weight of the antenna, pushing downwards, or pulling upwards, depending on the elevation angle. Specifically in small portable terminals, the compact elevation mechanism, including the motor, must deal with an antenna that for performance reasons is relatively large. This can have a negative effect on the performance and reliability of the motor. In some of the systems with intermediate gears, as e.g. in the case of U.S. Pat. No. 4,725,843, the pressure acts sideways on the motor axle. In a direct-coupled system this pressure will act in the axial direction of the driving motor.

Re polarization:

An example of the conventional practice is U.S. Pat. No. 4,907,003. A servomotor is used to turn the entire feed assembly and a regular potentiometer is employed for polarization angle indication.

The mechanics of the current invention differ from the above mentioned patent in that the feed is cross-polarization compensated and must stay fixed. Thus the OMT is rotated with respect to the feed which requires the use of a rotary joint.

Re angular sensors:

An important aspect of antenna positioners is an accurate indication of the current azimuth, elevation and polarization angle. Those data serve as feedback for the initial pointing in the auto-acquire process.

Such feedback should preferably be in the form of an electrical quantity, such as voltage. The patents mentioned above, concerned primarily with mechanics, do not address this. However, there are several patents dealing with motorized antenna alignment using such an approach, namely by employing potentiometers. Examples of these are U.S. Pat. No. 4,665,401, U.S. Pat. No. 4,907,003, U.S. Pat. No. 6,049,306, U.S. Pat. No. 6,937,119, U.S. Pat. No. 5,594,460 to cite a few. The approaches appear to use “regular” potentiometers as angular sensors, mostly driven indirectly by gears or cables from the drive motor.

The disadvantage of the above solutions is the relatively low accuracy and resolution of regular potentiometers and the potential slippage or backlash depending on the method of mechanical coupling to the potentiometers.

SUMMARY OF THE INVENTION

The invention, as described above in detail, contains improvements over the prior art in the azimuth, elevation and polarization mechanisms for motorized antenna positioners, as follows:

-   -   An azimuth drive, using a crossed cable and a driving pulley         with an undersized groove to clamp the wire with greater force         and provide more traction to the driven rotational platform with         the antenna. A single, rather than multi-turn, wrap around the         drum of the platform is used in two horizontal guiding channels.         This results in a very flat unit that can be mounted as lid on         the top of a typical baseband unit in a portable satellite         terminal.     -   An azimuth angle sensor using a circular potentiometer with         large circumference thus providing better accuracy, resolution         and freedom from slippage or backlash compared to prior art.     -   An elevation adjustment mechanism with a de-coupling feature         that isolates the elevation motor from the force exerted by the         antenna on the elevation assembly.     -   A polarization adjustment mechanism incorporating a polarization         angle sensor using a circular potentiometer. As in the azimuth         part of the positioner, better accuracy, resolution and freedom         from slippage or backlash is obtained compared to prior art

This invention includes an azimuth drive and azimuth angle sensor for use in a motorized antenna positioner for a small portable satellite terminal. The drive mechanism is sufficiently robust to reliably turn a 1 m antenna while having a very low profile. That enables the azimuth drive to be incorporated in the box housing the terminal's electronics without significantly affecting its dimensions. The novel angular sensor has improved accuracy and resolution over prior art.

The invention also includes an elevation drive for use in a motorized antenna positioner for a small portable satellite terminal. The elevation drive has a novel feature where the pressure due to the antenna weight applied to the elevation rod is transferred to the motor housing instead of acting on its axle. This is achieved by means of a bearing imbedded in the top cover of the motor housing.

The elevation drive has an elevation motor assembly having a housing, a motor and a motor axle. The motor assembly is mounted to a hinge on the rotatable platform.

The housing supports a bearing, which is engaged with said elevation rod such that said elevation rod may rotate freely about its axis relative to said housing. The elevation rod is coupled to the motor axle such that rotation of the motor causes rotation of the elevation rod. A threaded nut mounted to the antenna is threadably engaged with said the elevation rod such that rotation of the elevation rod causes the threaded nut to move longitudinally along the elevation rod causing a change in the angle of elevation of the antenna. Any force applied longitudinally along the elevation rod, for example due to gravity or wind acting on the antenna, is transferred through the bearing to the housing.

The invention further includes a polarization adjustment drive and angle sensor for use in a motorized antenna positioner for a small portable satellite terminal. The novel aspect of the polarization adjustment assembly is its angular sensor that, similar to the one in the azimuth unit, has improved accuracy and resolution over prior art.

The polarization adjustment drive and angle sensor includes a fixed part to which is mounted the feed. There is a rotatable part connected to the fixed part, the rotatable part rotatable about an axis relative to the fixed part. There is an OMT and LNB mounted to the rotatable part such that the OMT and LNB rotate about the axis with the rotatable part. A rotary potentiometer is attached to the fixed part having a circular conductive trace and a circular resistive trace concentric about the axis and fixed relative to rotation of the rotatable part. A plunger attached to the rotatable part traces a circular path as the rotatable part rotates about the axis, and is positioned such that it contacts the rotary potentiometer at a point of contact and connects the circular traces together. A circuit is connected to the potentiometer and applies a constant current to one end of the circular resistive trace and one end the circular conductive trace and outputs a voltage, indicative of the position of the plunger. The feed is aligned so as to receive a signal along the axis, and the OMT is aligned so as to receive a signal from the feed.

In its preferred embodiments, the current invention is applied to small portable satellite terminal antenna applications and it addresses the azimuth drive problems while keeping the structure flat. This is desirable for mounting considerations and very important for overall size and weight of the terminal.

The current invention provides a solution that is free of backlash or slippage.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will be apparent from the following detailed description, given by way of example, of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:

FIG. 1 depicts a portable satellite terminal;

FIG. 2 shows a front view of the antenna with its boom;

FIG. 3 depicts the components of the boom and feed assembly;

FIG. 4 shows the details of the boom attachment to the reflector;

FIG. 5 is a close-up view of the azimuth and elevation adjustment mechanism, showing the antenna mounted on the azimuth rotational platform and the attachment of the elevation adjustment mechanism;

FIG. 6 depicts the baseband unit with the embedded azimuth drive mechanism, with the antenna removed;

FIG. 7 shows a side view of the compact azimuth drive mechanism;

FIG. 8 depicts the pulley, cable and drum of the azimuth drive;

FIG. 9 shows the details of how the driving cable is terminated on the drum of the azimuth wire drive;

FIG. 10 is a side view of the pulley and drum assembly, showing the guiding channels (grooves) on the drum;

FIG. 11 depicts the cable with its terminations

FIG. 12 is a detailed drawing of the whole azimuth positioner assembly;

FIG. 13 shows the construction of the rotary sensing potentiometer;

FIG. 14 depicts the elevation adjustment mechanism in its deployed state;

FIG. 15 shows the internal details of the drive unit with rotational coupling, and linear de-coupling, between the motor axle and the elevation rod;

FIG. 16 is an outside view of the motor housing on hinge to be attached to the azimuth rotational platform;

FIG. 17 shows a cross-section of the upper boom arm assembly with the feed, OMT and polarization motor; and

FIG. 18 is an enlarged view of FIG. 17, focusing on the components of the subsystem for polarization adjustment.

DETAILED DESCRIPTION OF THE INVENTION

The antenna positioner and sensing mechanisms of this invention are preferably part of a portable communication unit capable of transmitting/receiving high-speed data and broadcast quality video via satellite. However, they may be used in a wide variety of settings and applications. To achieve good performance while preventing undue interference to or from other systems, a 1-meter parabolic antenna is preferably employed, together with a powerful RF amplifier. For ease of setup, the unit preferably contains all the necessary hardware and software for automatic acquisition of the desired satellite.

As shown in FIG. 1, the communication unit 100 is a portable satellite terminal consisting of a 1 m diameter parabolic segmented antenna 101 with a boom assembly 102 with a feed horn and receiver assembly 103 mounted on the end. The boom assembly 102 breaks into two parts for disassembly and transport. On the lower back part of the antenna 101, the RF transmit (Tx) electronics assembly 104 is mounted to a U-shaped carrier 502 (see FIG. 5). When the communications unit 100 is deployed, as shown in FIG. 1, the antenna 101 and RF transmit electronics assembly 104 are mounted on the baseband housing 105 (i.e. the housing for the “non-RF”, or “baseband” (BB) electronics). The baseband housing 105 has a main body 108 and foldable legs 106, which together with the main body 108 act as a tripod, providing a stable platform for the communication unit 100. The top of the housing contains the positioner elements for azimuth and elevation adjustment to which the antenna is attached. The polarization adjustment element is physically separated from the azimuth/elevation elements and is part of the feedhorn/receiver assembly 103 at the end of boom assembly 102.

As shown in FIG. 2, antenna 101 breaks into six segments 110 specially shaped for rigidity and compact stowage. The Transmit RF electronics assembly 104 remains attached to the back of the “main” segment 112. The boom assembly 102 connects to a U-shaped carrier 502 (see FIG. 5) behind the main segment 112.

FIG. 3 shows the two parts of the boom assembly 102. The upper boom assembly consists of boom arm 301 with feed 302, Transmit/Receive separator (OMT) 303 and receiver (LNB) 304. The feed, OMT and LNB are rotated for polarization alignment by motor and gear 305, with manual override 306. The Transmit port of the OMT is connected, via flexible waveguide 307, to solid waveguide 308 running inside the boom arm 301. The boom arm is terminated with a quick connect device that will attach the above-described assembly to the waveguide flange 310 of the lower boom arm 311. The lower boom arm is terminated with another quick-connect device 312 (e.g. screw-on), which connects to the U-shaped carrier 502 (see FIGS. 4 and 5).

FIGS. 4(a) and 4(b) show that the quick-connect device 312 on the lower boom arm 311 attaches to the flange, 402, mounted on the U-shaped carrier 502, which in turn is mounted on the main reflector segment 112.

FIG. 5 shows the antenna 101 mounted to the baseband housing 105.

The main reflector segment 112 is attached to the U-shaped carrier 502 on which is mounted the RF transmit (Tx) electronics assembly 104. The U-shaped carrier 502 also has connected to it the elevation assembly of the antenna positioner, namely threaded nut 504, with elevation rod 505 and elevation motor 506. The whole antenna assembly (antenna 101, RF transmit (Tx) electronics assembly 104, U-shaped carrier 502, and the elevation assembly of the positioner) is pivotally mounted, via hinges 507 and 508, on the rotational platform 509 for azimuth alignment driven by the drive unit 510. This platform and the motor are parts of the azimuth assembly of the positioner that in turn is part of the baseband housing 105.

FIG. 6 shows the baseband housing 105 with the legs 106 folded, after removal of the antenna assembly (not shown) from rotational platform 509 of the positioner. The baseband housing 105 contains the components needed to process data to and from a laptop computer or similar device into a form suitable for the Transmit RF electronics assembly 104 on the back of the antenna and the feed horn and receiver assembly 103. Attachment points 602 are for the attachment of the hinges 507 (see FIG. 5). Attachment point 603 is for attaching the elevation hinge 508 (see FIG. 5).

The azimuth, elevation and polarization elements of the positioner are now described in detail as follows:

The azimuth positioning mechanism (see FIGS. 7-12) employs a wire drive and comprises:

a) Drive unit 510 consisting of the step motor 701 that propels driving pulley 703 via gear reduction box 702. Motion is translated to drum 704 by the use of flexible wire 705. Drum 704 and plate 707 form part of previously mentioned rotational platform 509 that carries the antenna assembly and thus provides antenna azimuth angle adjustment.

b) Driving pulley 703 with groove 1001, undersized relative to the wire size, to capture the wire 705, thus clamping the wire with greater force as the wire is tightened creating a substantially higher rotating moment transfer. The crossed wire results in a 300 degree winding angle around the drive pulley. These two factors make it possible to drive the antenna load with a single wrap around the pulley and drum, compared to multiple wraps of greater than 360 degrees around a solid or helical drive shaft that are otherwise needed to drive said antenna load according to the prior art.

c) Drum 704 with two guiding channels 1002 and 1003 and two openings 902 and 903 for wire termination;

d) Flexible cable 705, with one end secured to the first drum termination point 902, running inside the first drum guiding channel 1002 with 200 degree winding angle, traveling to driving pulley 703 and resting inside undersized groove 1001 with 300 degree winding angle, traveling back to drum 704; running inside the second drum guiding channel 1003 with a 200 degree winding angle, and second end secured to the second drum termination point 903.

In a preferred embodiment, commercial quality “aircraft grade” type cable strand 7×19 is used. It consists of 1 center core bundle of 19 wires, which is straight, and 6 bundles of 19 wires helically stranded around the core. This provides the strongest and most flexible of cables, with greatest stretch. The stretch is compensated by springs (1101,1102) tensioning the cable terminations. The choice of cable is important to provide the friction needed for the drive pulley to drive the drum with the antenna assembly without slipping.

The whole assembly as described above is mounted on baseplate 706 which in turn is part of baseband housing 105.

FIG. 12 shows a more detailed drawing of the entire azimuth positioning unit. Motor 701 and gearbox 702 with pulley 703 are joined by coupler 1201. The other side of the motor axle is equipped with a hand wheel 1202 for manual override. The drive assembly is covered by cover 1203. Power to the motor is brought through waterproof strain relief feedthrough 1215.

Skirt 1204, with thrust washer 1205 on top of it, envelopes drum 704 and is attached to baseplate 706. It contains slots 1206 for the entry of the previously mentioned flexible cable 705 (see FIGS. 7-11). Drum 704 is attached to, and turns with, the upper part of bearing 1207 that fits into circular opening 1208 in baseplate 706. The lower part of bearing 1207 is attached to bearing plate 1209. Bearing plate 1209 also carries rotary sensing potentiometer 1210, and is attached to the underside of baseplate 706. Plate 707 is attached to drum 704 to form rotational platform 509 carrying the antenna assembly via attachment points 602, 603 and hinges 507, 508 as shown in FIGS. 5 and 6. Plate 707 also carries the waterproof strain relief feedthrough subassembly 1212 with a connector plate and gasket. This allows external wiring to be brought through opening 1208 to the baseband unit 105 on which baseplate 706 is mounted. Baseplate 706 also contains spirit level 1214 for help with setup.

As can be seen in FIG. 5, the above-described azimuth positioner construction results in a very flat unit that adds little additional height to the baseband unit. This facilitates compact stowage of the terminal as a whole.

The Azimuth angle indicator (see FIGS. 12 and 13) consists of:

a) Rotary potentiometer 1210 with self-adhesive backing, attached to bearing plate 1209. As shown in FIG. 13, it is made up of two dielectric layers 1301 and 1302, one of which contains a circular conductive trace 1303 serving as the potentiometer wiper and the other a resistive circular trace 1304, said traces being on the adjacent sides of the dielectric layers that are separated by a spacer layer 1305.

Similar devices are commercially available, for example from Spectra Symbol, of Salt Lake City, Utah.

b) Plunger subassembly 1213 (see FIG. 12) where a spring-loaded plunger in a tubular carrier is attached to the underside of drum 704. The plunger connects the said traces of potentiometer 1210 together directly underneath, due to the downward pressure of said plunger, thus enabling the wiper action, as demonstrated in FIG. 13.

c) A circuit is (not shown) connected to the linear end of rotary sensing potentiometer 1210. The circuit is mounted on the underside of baseplate 706 and protected by cover 1211. The circuit applies dc voltage to the two ends of the resistive trace in potentiometer 1210 and outputs the voltage between the conductive trace 1303 and one of the said ends of the resistive trace 1304 to an Analog-to-Digital Converter (ADC) connected to the circuit. This voltage is proportional to the angle of rotation of drum 704. The said ADC converts this voltage value from its analog form to a digital value for further processing by the terminal's computer. In the preferred embodiment the ADC is a 10-bit device, therefore, theoretically the voltage will be represented by 2¹⁰=1024 values. Of this, the actual usable range is closer to about 800, so each 1-bit step corresponds to 360/800=approximately a 0.5 degree change in the antenna azimuth direction. To insure accurate correlation with the real antenna position, a calibration process is used with the aid of the communication unit's software.

The design described above has the advantage over the prior art in that is provides more accurate indication of the antenna azimuth angle, with better resolution and freedom from slippage or backlash.

The elevation adjustment mechanism of the positioner (see FIGS. 14 to 16) consists of:

a) Elevation motor assembly 506, pivoting on elevation hinge 508 which is attached to azimuth rotational platform 509,

b) Elevation rod 505 connected to the motor axle inside motor assembly 506, and with its threaded upper portion connected to gear

c) Gear 504 that is essentially a nut that pivots about an axle turning between the two right-angled corners of U-shaped carrier 502.

FIG. 15 shows the details of the coupling between the elevation rod and the motor. Motor 1501 is centred within main housing 1502. Elevation rod 505, with hand wheel 1509 for manual override, is press-fitted into ball bearing 1503 which in turn is attached to lid 1504. The lower end of elevation rod 505 is connected to axle 1505 of motor 1501 by coupler 1506, with set screw 1507. With bearing 1503 holding elevation rod 505, the push or pull by the antenna on rod 505 is diverted from motor axle 1505 onto housing 1502 through bearing 1503 and lid 1504.

The power to the motor is brought through connector 1510. Housing 1502 is held on elevation hinge 508 by means of axle 1511, around which the whole elevation assembly pivots. Hinge 508 is attached to the Az/El Plate 707 of the azimuth rotational platform 509 by means of guiding pins 1601 and hand screw 1602 shown in FIG. 16.

The decoupling of the motor from the elevation rod achieved by the above design results in better and more reliable performance of the motor and thus the entire elevation adjustment mechanism.

The polarization adjustment mechanism of the positioner is built into the feed/OMT subassembly mounted on the upper boom arm assembly as depicted in FIG. 3. FIGS. 17 and 18 provide additional details specifically with respect to the polarization adjustment mechanism itself.

FIG. 17 is a cross-sectional side-view of the feed/OMT assembly showing feed 302, OMT 303 and polarization motor 305 with hand wheel 306 for manual override. Also shown is the Rx reject filter 1701 in the Tx waveguide 1702 with the latter terminated by flange 1703.

From there, a flexible waveguide (not shown) connects to the lower flange on the OMT.

FIG. 18 is an enlarged view of the interface of feed 302, OMT 303 and polarization motor 305, showing the relevant parts of the polarization adjustment mechanism. Since the feed is a cross-pol compensated type that must not be rotated, a rotary joint is used to connect the feed to the OMT, thus enabling OMT rotation with respect to the feed for polarization adjustment.

As shown in FIG. 18, OMT 303 is attached to rotating part 1801 of the rotary joint and the feed 302 is attached to fixed part 1802. Rotating part 1801 carries main driven gear 1803, engaged with interface gear 1804, which in turn is driven by driver gear 1805, attached to the axle of polarization motor 305. Thus when the motor turns, OMT 303 and rotating part 1801 of the rotary joint turn with respect to the stationary feed.

The flange of the feed has attached to it the circular part of rotary sensing potentiometer 1806. The potentiometer is of the same type as the one for azimuth adjustment, but of different size. The rotating part 1801 of the rotary joint has mounted on it spring-loaded plunger 1807, pushing on the potentiometer and enabling the wiper action. The linear part 1808 of the potentiometer contains the input/output traces and connects to a cable that also provides power to motor 305. The cable terminates in connector 1704 (FIG. 17). Thus at this connector a voltage proportional to the polarization angle is available for feedback to the auto-acquire system of the terminal. Again, as in the case of the azimuth sensor, this analog voltage can be converted to a digital form for further processing. With a 10-bit ADC, 0.5 degree steps in polarization angle are obtained. As in the azimuth sensor case, this method provides better accuracy and resolution and freedom from of slippage or backlash compared to more conventional approaches. 

1. An azimuth drive and sensor for a satellite terminal, comprising: a driving pulley; a motor connected to said driving pulley, said motor operative to drive said driving pulley; a rotatable platform for mounting an antenna, wherein said rotatable platform is rotatable about an axis; a flexible wire engaged with said rotatable platform and said driving pulley such that rotation of said driving pulley causes rotation of said platform; a rotary potentiometer having two dielectric layers, a first one of said dielectric layers having a circular conductive trace and a second one of said dielectric layers having a circular resistive trace, said circular traces being adjacent to one another and separated by a spacer layer, said circular traces being concentric about said axis and lying in a plane perpendicular to said axis, wherein said potentiometer is fixed relative to rotation of said platform; a plunger attached to said rotatable platform, said plunger positioned such that it traces a circular path when said platform is rotated about said axis and such that said plunger contacts said rotary potentiometer at a point of contact and connects said circular traces together at said point of contact; and a circuit connected to said potentiometer which generates an output voltage proportional to an angular position of said plunger which angular position indicates an azimuthal angle of an antenna.
 2. An azimuth drive according to claim 1, wherein said driving pulley has a groove extending about its circumference and wherein flexible cable is engaged with said groove for a 300 degree winding angle around the drive pulley.
 3. An azimuth drive according to claim 1, wherein said rotatable platform has a first guiding channel and a first termination point and a second guiding channel and a second termination point, said termination points for connecting respective ends of said flexible cable, and each of said guiding channels for engaging a portions of said flexible cable proximate a respective one of said ends.
 4. An azimuth drive according to claim 3, wherein said flexible cable is engaged with said first guiding channel for a 200 degree winding angle around said rotatable platform and wherein said flexible cable is engaged with said second guiding channel for a 200 degree winding angle around said rotatable platform.
 5. An azimuth drive according to claim 1, wherein said flexible cable is aircraft grade type cable strand 7×19.
 6. An azimuth drive according to claim 3, wherein said termination points include springs for tensioning said flexible cable.
 7. An azimuth drive according to claim 1, wherein said flexible cable is crossed between said driving pulley and said rotatable platform.
 8. An azimuth drive according to claim 1, wherein said circuit comprises an analog to digital converter that converts said second voltage from analog form to digital form.
 9. An azimuth drive according to claim 8, wherein said analog to digital converter is a 10-bit analog to digital converter.
 10. An azimuth drive according to claim 1, wherein said drive unit, said pulley, and said rotational platform form part of a baseplate, said baseplate being an approximately planar upper surface of a baseband housing, said baseband housing containing components required to process data between said satellite terminal and a computer.
 11. An azimuth drive according to claim 1, wherein said plunger is spring loaded.
 12. An azimuth drive according to claim 1, wherein said motor is a step motor.
 13. An azimuth drive according to claim 1, wherein said motor is connected to said driving pulley by a gear reduction box.
 14. An azimuth drive according to claim 2, wherein said groove is an undersized groove relative to a diameter of said flexible cable.
 15. An azimuth angle sensor for a satellite terminal, comprising: a platform for mounting an antenna, said platform rotatable about an axis, a rotary potentiometer having two dielectric layers, a first one of said dielectric layers having a circular conductive trace and a second one of said dielectric layers having a circular resistive trace, said circular traces being adjacent one another and separated by a spacer layer, said circular traces being concentric about said axis and lying in a plane perpendicular to said axis, wherein said potentiometer is fixed relative to rotation of said platform; a plunger attached to said platform, said plunger positioned such that it traces a circular path when said platform is rotated about said axis and such that said plunger contacts said rotary potentiometer at a point of contact and connects said circular traces together at said point of contact; a circuit connected to said potentiometer which generates an output voltage proportional to an angular position of said plunger, which angular position indicates an azimuthal angle of an antenna.
 16. The angle sensor of claim 15, wherein said plunger is spring loaded.
 17. The angle sensor of claim 15, wherein said potentiometer and said rotatable platform are mounted on a baseband housing of said satellite terminal.
 18. The angle sensor of claim 15, wherein said circuit includes an analog-to-digital converter that is part of said circuit, that converts said second voltage from analog to digital form.
 19. The angle sensor of claim 15, wherein said rotary potentiometer, said platform and said circuit form part of a baseplate, said baseplate being an approximately planar upper surface of a baseband housing, said baseband housing containing components required to process data between said satellite terminal and a computer.
 20. An elevation drive mechanism for changing an angle of elevation of an antenna of a satellite terminal, wherein when said angle of elevation is changed said antenna is pivoted about a first axis, said elevation drive mechanism comprising: an elevation motor assembly having a housing, a motor and a motor axle, said motor assembly pivotable about a second axis; a threaded elevation rod having a longitudinal axis, said elevation rod coupled to said motor axle such that rotation of said motor axle causes rotation of said elevation rod; a bearing supported by said housing, said bearing engaged with said elevation rod such that said elevation rod may rotate about said longitudinal axis relative to said housing; a threaded nut, said threaded nut pivotally mounted to said antenna so as to permit said threaded nut to pivot about a third axis, said nut threadably engaged with said elevation rod such that rotation of said elevation rod about said longitudinal axis causes said threaded nut to move longitudinally along said elevation rod causing a change in said angle of elevation; wherein a force applied longitudinally along said elevation rod is transferred through said bearing to said housing; and wherein said first axis, said second axis and said third axis are parallel to one another.
 21. An elevation drive mechanism according to claim 20, wherein said elevation rod is coupled to said motor axle by a coupler.
 22. An elevation drive mechanism according to claim 20, wherein said force is caused by one of gravity and wind.
 23. An elevation drive mechanism according to claim 20, further comprising a manual override to permit manual rotation of said elevation rod.
 24. An elevation drive mechanism according to claim 20, wherein said elevation rod is in press-fitted engagement with said bearing.
 25. An elevation drive mechanism according to claim 20, wherein said bearing is a ball bearing.
 26. A feed assembly and polarization angle sensor for a satellite terminal, comprising: a fixed part; a feed mounted to said fixed part; a rotatable part connected to said fixed part, said rotatable part rotatable about an axis relative to said fixed part; a Transmit/Receive separator and a receiver mounted to said rotatable part such that said Transmit/Receive separator and said receiver rotate about said axis with said rotatable part; a rotary potentiometer attached to said fixed part, said potentiometer having two dielectric layers, a first one of said dielectric layers having a circular conductive trace and a second one of said dielectric layers having a circular resistive trace, said circular traces being adjacent to one another and separated by a spacer layer, and said circular traces being concentric about said axis and fixed relative to rotation of said rotatable part; a plunger attached to said rotatable part such that said plunger traces a circular path as said rotatable part rotates about said axis, said plunger positioned such that it contacts said rotary potentiometer at a point of contact and connects said circular traces together at said point of contact; a circuit connected to said potentiometer which generates an output voltage which corresponds to an angular position of said plunger which angular position indicates a polarization angle of an antenna; wherein said feed is aligned so as to receive a signal along said axis, and said Transmit/Receive separator and said receiver are aligned so as to receive a signal from said feed.
 27. A feed assembly and polarization angle sensor according to claim 26, further comprising a motor, said motor operatively connected to said rotatable part such that activation of said motor causes rotation of said rotatable part about said axis.
 28. A feed assembly and polarization angle sensor according to claim 26, wherein said feed assembly and polarisation angle sensor is mounted to a boom of a satellite terminal antenna.
 29. A feed assembly and polarization angle sensor according to claim 28, further comprising a gear on said rotatable part wherein said gear rotates with said rotatable part and wherein said gear is operatively connected to said motor such that activation of said motor causes rotation of said rotatable part about said axis.
 30. A feed assembly and polarization angle sensor according to claim 26, further comprising a manual override to manually rotate said rotatable part.
 31. A feed assembly and polarization angle sensor according to claim 26, wherein said feed is a cross-polarization compensated feed.
 32. A feed assembly and polarization angle sensor according to claim 26, wherein said plunger is spring loaded.
 33. A feed assembly and polarization angle sensor according to claim 26, wherein is said circuit includes an Analog-to-Digital Converter that converts said second voltage from analog to digital form. 